1. Technical Field
The invention relates to seismic prospecting and geological exploration, and more particularly to seismic prospecting in marshy areas lacking significant areas of dry ground.
2. Background Art
Land based seismic prospecting is a well established art. Generally, it requires at least one source fired to impart a signal into the ground, the signal is reflected by underground formations, and is received by at least one receiver. The received signal is then stored and analyzed to glean information about the underground formations.
Geologic exploration or prospecting operations of this sort generally require a close coupling between the source and the ground. Sources are frequently placed in shallow boreholes known as "shotholes" and coupled to the ground in the shothole. One common source is an explosive charge, which is commonly placed on the ground surface or at the bottom of a shothole and then detonated at a predetermined time. As with all basic types of sources, a firm coupling with the ground is required.
Marshy areas present particular problems in land based seismic prospecting or exploration, especially with respect to coupling. The current approach to positioning explosive charges is to place them in a hollow metal tube at the end of some pipe stem, push the charge into the damp, unstable soil as far as possible, and then deposit the charge. One unfortunate result from this approach is that it frequently results in poor coupling with the ground because the soil is too unstable. This in turn yields unreliable information about the underground formation. However, it is not possible to force the charge deeper with external force on the pipe stems at the surface without collapsing the cage and damaging the charge.
It is therefore a feature of this invention to provide a drill bit for use in marshy areas to obtain superior coupling between the charge and the ground.
It is a further feature of this invention that the bit is for use with non-rotating drilling.
It is still a further feature of this invention that it can employ a hammer-type approach to drilling.